Nextcloud client: Add 3.18.0 RC6

Signed-off-by: Álvaro Brey Vilas <alvaro.brey@nextcloud.com>

metadata/com.nextcloud.client.yml

@@ -1704,6 +1704,7 @@ Builds:
 
   - versionName: 3.18.0 RC5
     versionCode: 30180055
+    disable: obsolete RC
     commit: rc-3.18.0-05
     sudo:
       - apt-get update || apt-get update
@@ -1721,6 +1722,25 @@ Builds:
     scandelete:
       - src/androidTest
 
+  - versionName: 3.18.0 RC6
+    versionCode: 30180056
+    commit: rc-3.18.0-06
+    sudo:
+      - apt-get update || apt-get update
+      - apt-get install -y openjdk-11-jdk-headless
+      - update-alternatives --auto java
+    gradle:
+      - generic
+    rm:
+      - user_manual
+      - gplay.gradle
+    prebuild:
+      - mkdir -p $HOME/.gradle
+      - echo org.gradle.jvmargs=-Xmx9g -XX:MaxMetaspaceSize=512m -XX:+HeapDumpOnOutOfMemoryError
+        > $HOME/.gradle/gradle.properties
+    scandelete:
+      - src/androidTest
+
 MaintainerNotes: 'Latest 3 stable version will be kept, RC versions will be directly
     outdated by either a new RC or by a stable version: 3.3.0 RC1 -> 3.3.0 RC2 ->
     3.3.0 (stable)'